OpenSSF/OSV advisory MAL-2026-13745 confirms this npm version as malicious. base65-11x is a name-lookalike of the widely used base-x encoder. Both entrypoints (src/cjs/index.cjs and src/esm/index.js, ~127KB each vs. ~4KB for real base-x) contain the legitimate base-x source followed by a ~123KB single-line obfuscated payload wrapped in a custom-VM IIFE (identifiers vmN, vmA_ab9191, vmU_d6a896; Object.defineProperty-based dispatch on a global slot)...
Source
OpenSSF Malicious Packages via OSV
Summary
Malicious code in base65-11x (npm)
Details
base65-11x is a name-lookalike of the widely used base-x encoder. Both entrypoints (src/cjs/index.cjs and src/esm/index.js, ~127KB each vs. ~4KB for real base-x) contain the legitimate base-x source followed by a ~123KB single-line obfuscated payload wrapped in a custom-VM IIFE (identifiers vmN, vmA_ab9191, vmU_d6a896; Object.defineProperty-based dispatch on a global slot). The payload sits at module top level, so it executes automatically whenever a consumer require()s or import()s the package. A pure base-encoding utility has no functional need for runtime-VM-packed code on load, and the payload is duplicated across CJS and ESM entrypoints to ensure execution regardless of module system. The specific payload behavior is concealed inside the VM interpreter and cannot be recovered without executing it.
Decision reason
No blocking static signals were detected.